Signaling apparatus and circuit



(No Model.)

B. J. HALL 8z. I. A. PIGKERNE LL.

SIGNALING APPARATUS AND CIRCUIT.

Patented Feb. 28, 1893'. Hg].

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EDWARD J. HALL, OF MORRIS, AND FRANK A. PICKERNELL, OF NEWARK,

NEW JERSEY, ASSIGNORS TO THE AMERICAN TELEPHONE AND TELE- GRAPH COMPANY,OF NEW YORK.

SIGNALING APPARATUS AND CIRCUIT.

-L.PECIFICATION forming part of Letters Patent No. 492,482, datedFebruary 28, 1893. Application filed October 13, 1892. Serial No.448,766. (No model.)

To all whom it may concern:

Be it known that we, EDWARD J. HALL, residing at Morris township, in thecounty of Morris, and FRANK A. PICKERNELL, residing at Newark, in thecounty of Essex. State of New Jersey, have invented certain Improvementsin Signaling Apparatus and Circuits, of which the following is aspecification.

This invention relates to call generators for telephone exchanges, totheir circuits, and to devices forgraduating, controlling anddifferentiating their currents.

It frequently becomes necessary and more frequently desirable, in theoperation of telephone circuits to have a magneto receiving telephone,and a call bell in circuit at the same time, so that whether words orcalling currents are transmitted at the distant station, either maywithout delay be received and attended to; this contingency howeverrequires that the telephone shall be at the ear of the attendant. v

In the specification of a separate application for Letters Patent, filedof even date herewith by Edward J. Hall, Serial No. 448,762 anddescribing a system of divided switchboards, with office trunkconductors, and meansfor operating and interconnecting a series ofsubstation circuits upon said switchboards, such a desirability isadverted to, and

- we have shown as one mode of carrying out the operation of signalingthe substation called for, apparatus, whereby as soon as the operator atone switchboardhas called for a line at the other, the call generatorterminals by means of a suitable key or switch at the first switchboardmay be united to the trunk conductors to which the line at the secondswitchboard is to be united. As soon therefore as the second switchboardconnection is made, the bell of the desired station is rung, while thetelephone at the calling station which has been introduced into thecircuit to give the order, is still held to the ear of the persondesiring communication; and not only is this the case, but after theattendant at the second substation has brought his telephone into thecircuit to see what is wanted and to exchange conversation, the callgenerator at the central station may remain connected with the talkingcircuit and continue to send call signals over the line, and throughboth substation telephones, until the operator, havingfinished otherbusiness taken up ad in terim, returns to this connection, and turns thegenerator switch, thus disconnecting the call generator.

Heretofore when a receiving telephone has either deliberately orinadvertently been left in circuit during the operation of sending acall signal by means of a magneto generator, the telephone has uniformlybeen fully responsive to said generator and the instrument has been soaffected by the circulation of the call currents through its helices, asto emit intensely loud and rattling sounds, representing such currents,and productive of great discomfort to the person at whose ear the saidtelephone is held.

The purposes of our present invention are twofold: The first is toprovide means for ringing polarized bells by means of alternatingcurrent magneto electric generators or equivalent apparatus,withoutmaterially affecting speech receiving instruments included in the samecircuit; and the second is to furnish efficient means whereby a callgenerator common to a number of switchboard connecting cords, some ofwhich may be channels for voice currents, and other simultaneouslyforming conductors for the call currents of said generator, may beemployed Without involving telephonic interference, or the transit ofvoice currents between any two such cords. In attacking the problemstated by the first of these purposes, a study of the followingconsiderations have been found useful. Electrical impulses succeedingone another at a com paratively low rate of speed, say fifteen persecond as is usually the case with those employed in call'signals fortelephonestations,

are when regular and uniform, virtually in-jaudible in a telephone. Thereason why with an ordinary generator they are audible, is that thecurve representing the electromotive force is irregular and rapidlychanging, so

that instead of fifteen impulses per second, a very much larger numberis produced. The sharp and ragged points in the curve of electromotiveforce would correspond to harmonics obtained from causing a tuning forkto vibrate through an amplitude greater than that required by itsfundamental. We attain the desired object by associating with thecircuit including the bell which is to be affected, and the telephonewhich is not to be affected, a call generator graduated by the suitableapplication of retardation coils or electromagnetic resistances andcondensers, in such a manner that the currents it develops have thecrests of their alternations so rounded, that while continuing toefficiently operate polarized bells, they produce no material sound intelephones. We connect the condenser between the two generator mainconductors near the terminals thereof, so that it forms an electrostaticshunt therefor; and between each of the said terminals, and the junctionof the condenser shunt, we include in circuita suitably proportionedretardation coil or electro-magnetic resistance having few convolutionsand therefore little real resistance, but also containing in its coreand casing, a large amount of iron, and therefore a high apparentresistance d ue to self-induction.

To carry out the second part of the invention, the generatormainconductors have auxiliary or branch conductors, leading in pairs, tokeys having each a connection with some one of a number of switchboardconnecting cords which are used to unite any two circuits for throughcommunication; and in the circuit of both conductors of each pair ofsuch auxiliary conductors are placed retardation coils orelectromagnetic resistances wound with a comparatively large number ofconvolutions, so as to offer a relatively high real resistance; butcontaining comparatively little iron, wherebythey are enabled to offeranapparent resistance attributable to self-induction, relatively high tovoice currents, and relatively low to calling currents. It may here beexplained that helices or coils of wire which surround or are surroundedby iron,oif'er by reason of their self-induction a high retardation orapparent resistance both to the cal-l currents and to voice currents,since these both undergo a constant change, generally by alternatingtheir direction; this apparent resistance largely depends upon theamount of iron contained in the coil. But the rate of change is muchhigher in the voice currents, than it is or can be in the call current,and the apparent resistance offered by a given construction of coil isalso largelydependent on such rate; hence though by reducing the amountof iron contained in the coils, the apparent resistance they offer tothe call currents which have a low rate of change can be greatlydiminished, until in fact it closely approximates the real resistanceonly; the said reduction of iron does not materially diminish theapparent resistance offered to voice currents whose rate of change is somuch higher. The graduating electromagnetic resistances in the generatormains which are to affect the call currents, are for this reason made tocontain alarge amount of iron,while the circuit differentiatingelectromagnetic resistances in the auxiliary conductors which areintended to oppose the passage of the voice currents only, whileaffording an unopposed passage to call currents, are therefore made tocontain little iron.

In the drawings which illustrate and form a part of this specification,Figure 1 is a diagram showing the invention applied to a simpletelephone circuit of two stations. Fig. 2 is a similar diagramindicating conventionally a compound telephone circuit extending betweentwo stations through a third. Fig. 3 is a detail diagram indicatinginfull, theconnections of a call generator by means of suitable call keysand connecting cords with telephone circuits. Fig. 4 is a diagramshowing a converter interposed between the generator proper and itsworking circuits. Fig. 5 is a diagram illustrative of the second featureonly of the invention.

In Fig. 1 we have an electric circuit C, having direct and returnconductors L and L and extending between two telephone stations A and B.At A a graduated magneto generator M, is included in the circuit; and atB there is a polarized bell b, and receiving and transmitting telephonest, 25 The direct conductor L, at B, connects at u with the usualautomatic telephone switch 8, on the hook of which the receiver t ishung, the circuit being supposed to be at rest. The telephone being thushung on the switch, the circuit continues through the said switch to thecontact 8 forming the terminal of the branch 6 which joins the returnmain conductor L at the point z, and in which is connected the bell b.The telephone branch 7 extends from the terminal contact 8 through thetelephones to the same point z, and is closed by the removal of thetelephone from the hook, the bell branch being at the same time opened.

Atstation Aa condenserc has its terminals 2 and 3 united with thecircuit conductors L and L respectivelyatac, and y,bridging them, andestablishing an electrostatic shunt round the generator; and anelectromagnetic resistance or retardation coil R is included in each ofthe generator mains 5 between the generator terminals and the condenserjunctions as and y. The said retardation coils are made with acomparatively few turns of wire, but contain in their cores and casingsa relatively large amount of iron. WVe have found coils having a real orconductor resistance of about forty ohms answer well. It is necessarythat the conductor resistance of these coils shall be low, in order thatthe currents developed by the generator M may be of sufficientvolume tosupply as many circuits as it may at any IIO '19 and plug terminals Pand P time be necessary to ring over at once. And it is also necessarythat there shall be a considerable amount of iron in and about thecoils, in order that their apparent resistance, or counterelectromotiveforce shall be sufficiently high to graduate the current, whereby it maybe caused to assume a character or form to which the telephone when incircuit is irresponsive. The several terms electromagnetic resistance,inductive resistance, retardation coil, choking coil and self inductioncoil have all been in the art applied to such coils R, which areintended to oppose the currents traversing them, an apparent resistancewhich is composed of their real resistance and their inductance, and weunderstand the said terms to be interchangeable.

WVe have found condensers, having a capacity of three microfarads, tooperate satisfactorily; and such a condenser, associated as described,with the retardation coils R, efficiently achieves the desiredgraduation.

In Fig. 2, the connections at both terminal stations are alike, and areidentical with those of station E in Fig. 1. Thetelephonetatstation B ishowever hung onits hook, and the circuit there is through the bell I);while at station E the telephone t is removed from the switch, andconsequently is in circuit. The two sections 0 and O of the circuit'areunited at a central or intermediate station D to form one compoundcircuit, having a bell in circuit at one station and a telephone incircuit at another. At D an alternating current call generator M,graduated as described above by retardation coils R and a condenser c,is connected in derived circuit or in multiple arc with the saidcompound telephone circuit, one of its main conductors 12 joining theconductor L of such circuit ate, and the other 13 joining the conductorL at w. Under these conditions the alternating currents of the graduatedgenerator M will sound the call in the bell b at B but will not disturbor produce sounds in the telephone tat B though both alike are in thecircuit and equally trav ersed by such alternating currents.

Fig. 3 indicates the connections of two pairs of switchcords F and Fwith the generator M. These may be regarded as being located either atdifferent sections of theswitchboards,

or at the same section; but some of the arrangements shown are necessaryonly, where they are at different switchboards. Hence the former view isthe one to be preferred.

0 and C are circuits leading from substations where are telephones t, tothe central station D where they are united by the flexible switchcordF, which has conductors p and Other two circuits 0 and O are in likemanner shown cord F its conductors p and p and terminal plugs P and P Mis the generator, 5 its main conductors, R its graduating retardationcoils, and 0 its graduating condenser. Branching from any points 9 h, onthe mains 5, are paired condoctors 12 and 13, leading to the severalswitchcords; and the generator may be common to any number of such pairsof conductors.

In the circuit of each member of each pair of conductors 12 and 13, isan auxiliary retardation coil 7". These retardation coils 7' containacomparatively small amount of iron, but are wound with a comparativelylarge number of turns of wire. We have satisfactorily used coils woundup to aconduotor resistancce of one hundred and fiftyohms. Theconstruction adopted for the coils r, readily permits the passage of thealternating call current of the generator; but the more rapidlyalternating telephonic currents are strongly opposed; the apparentresistance offered by such coils to voice currents being much greaterthan that offered to call currents. As soon therefore as the connectionis made at the connecting-board the bell at the desired station beingconnected with the generator will ring continuously until the attendantthere takes down his telephone and begins to talk. But when that isdone, though the generator connection continues, two persons talking atthe two connected stations are not disturbed thereby,because theirtelephones do not respond to the graduated call currents. The positionof coils r, in the circuits of the branched-conductors 12 and 13 isnecessary, as otherwise all circuits over which the ringing current wassimultaneously being sent will be telephonically cross-connected at theterminals of the retardation coils R, or at the branching points 9 h;but the interposition of the coils 0" which may be said to be opaque tovoice currents, presents an etfectualbar to the passage of suchcurrents, and virtually prevents such crossconnection so far as concernstelephonic transmission. i

N is a three way cam and spindle switch, which controls the connectionwith the switchcord conductors of the operators telephones, thegenerator circuits, and the disconnecting annunciator d.

When the said cam lever is turned to the side shown in connection withthe switchcord F, the operators telephones T T are con nected throughtheir terminal contacts eand c and the corresponding contacts we and Wof the bridge conductors 31 and 30, between the switchcord conductors pand p When the cam is turned into the opposite extreme position, thegenerator conductors 12 and 13' are by subbranches 14 and 15 and contactsprings 17 and 18 and corresponding contact springs n and n connectedwith the bridge conductors 30 and 31, and thereby with the switch cordconductors; and when the cam is caused to take the middle position, bothtele- IIC phones and generator are disconnected from the cords, and thedisconnecting drop (Z only is bridged across the circuit.

Fig. 4 differs only in slightparticulars from the organization shown inFig. 3. The cord and key connections are omitted as being identical, anda converter J is interposed between the generator M and the retardationcoils R and 4; one helix of the converter is joined up in a circuit '0with the armature coils, and the other has its terminals united to themain conductors 5. In this case, the generator and converter togethervirtually constitute the working generator. In some cases it isconceivable that the latter object of our invention namely the isolationor differentiation telephonically of the several cord circuits of thegenerator, is alone to be attained. In such cases the retardation coil Rand the condenser,may be dispensed with, and this is shown in Fig. 5,where the generator mains divide into their branch conductors at thepoints g and h without any previously interposed resistances orretardation coils; the coils 7' being however connected as usual, ineach of the branch conductors 12 and 13.

We have so far exclusively spoken of a magneto electric call generator,but we may of course substitute therefor any well known practicalequivalent thereof, such as a battery and pole changer, withoutdeparting from the spirit of our invention.

We claim- 1. The combination of an electric circuit; and a polarizedbell and magneto telephone included therein; with an alternating currentcall generator graduated to produce electrical currents adapted tooperate said bell, but to which the said telephone is irresponsive.

2. In an electric circuit, the combination substantially as hereinbeforedescribed, of a polarized electromagnetic bell; and a magneto telephone;with an alternating current call generator; and graduating devicestherefor, consisting of a condenser shunting the said generator, and anelectro-magnetic resistance included in the circuit between each pole ofthe generator and the condenser.

3-. A telephone circuit extending between two terminal stations throughan intermediate or central station; a receiving telephone and a callbell connected with said circuit at the said terminal stations; combinedwith an alternating current call generator connected with said circuitat the intermediate station; and graduating devices therefor, comprisinga condenser constituting an electro-static shunt for the said generator,and an electromagnetic resistance or retardation coil interposed betweeneach terminal of said generator and the condenser, whereby the currentsdeveloped by said generator are enabled to operate said bell without theproduction of disturbing sounds in the said telephone, substantially asdescribed.

4. The combination substantially as hereinbefore described, of anelectric circuit; a polarized electro-magnetic bell: and a magnetotelephone included therein; with a magneto electric generator, andgraduating devices therefor comprising a converter or induction coilhaving its secondary connected with the said electric circuit, and itsprimary included in a closed circuit with said generator; a condenserbridging or shunting the said secondary; and an electromagneticresistance included in circuit between the terminals of said secondary,and the terminals of said condenser bridge, substantially as described.

5. The combination with a series of telephone circuits, and call sendingkeys therefor; of a common call generator having conductors extending inpairs to said call keys; and a retardation coil in each of the saidgenerator conductors for preventing the passage of telephonic currentsbetween circuits simultaneously connected with any two pairs of the saidconductors, substantially as described.

6. The combination with a series of telephone circuits; and call sendingkeys therefor; of a common magneto call generator; a

series of pairs of conductors extending from the poles thereof to saidcall keys; and an inductive resistance or retardation coil constructedto offer a relatively low apparent resistance to call currents, and arelatively high apparent resistance to voice currents, included in eachof the said generator conductors; substantially as described.

7. The combination ,,with a series of telephone circuits, and callsending keys therefor; of an electric call generator common to theseries, having conductors extending to said call keys; and means asindicated. for preventing the passage of telephone currents throughtheir respective call keys, generator conductors, and common portions ofthe said generator circuit, between any two telephone circuits overwhich calls are simultaneously being sent.

8. The combination of a series of telephone main circuits converging toa central station; switchboard connecting cords at said station foruniting any two circuits; call sending keys one for each connecting cordincluded in circuit therewith; a common magneto electric call generatorhaving conductors extending in pairs to the said keys, and adapted to bethereby connected with the connecting cord circuit; and anelectromagnetic or retardation coil included in the circuit of each ofthe said paired. conductors, the said coils being so constructed as tooffer a relatively low inductive resistance to call currents, and arelatively high inductive resistance to voice currents,

substantially as and for the purposes specified.

9. The combination of a series of telephone circuits, each extendingfrom a substation to a central station;,a telephone and call bell ateach substation; switchboard conducting cords at the central station foruniting any two circuits; call keys one for each cord, connected incircuit therewith; a magneto call generator common to the series ofcircuits, having branch conductors in pairs extending from its terminalsto said call keys; main conductors connecting the generator termi nalsrespectively with their several branches;

a condenser shunting the generator a retardation coil in each mainbetween the generator terminal and the condenser; and an auxiliaryretardation coil in each branch conductor; substantially as describedand for the purposes specified.

In tcstimonywhereofI havesigned myname

